In a statement on Twitter, MGM Resorts said it had locked down hotels in the vicinity at the request of law enforcement officers. It was unclear if other casinos were also put on lockdown following the incident.

“Our thoughts and prayers are with the victims of last night’s tragic events. We’re grateful for the immediate actions of our first responders,” MGM Resorts said in the tweet.

Las Vegas’s casinos, nightclubs and shopping draw some 3.5 million visitors from around the world each year and the area was packed with visitors when the shooting broke out shortly after 10 p.m. local time (0400 GMT).